1. Field of the Invention
The present invention relates to a driving device for linear compressor which, for example, reciprocates a piston in a cylinder by means of a linear motor to generate a compressed gas in a compression chamber formed of the cylinder and the piston.
2. Related Art of the Invention
A linear compressor for generating a compressed gas using the elasticity of a mechanical elastic member or the compressed gas has been known.
Thus, the configuration and operation of a conventional linear compressor using a spring as an elastic member will be described with reference to FIG. 7, which is a view showing the configuration of a conventional linear compressor.
A cylinder 60 supports a piston 61 in such a manner that the piston 61 can slide along an axial direction thereof. The piston 61 has magnets 62 fixed thereto. Stator coils 64 embedded in an outer yoke 63 are disposed opposite to the magnets 62.
A compression chamber 65 formed of the cylinder 60 and the piston 61 has a suction pipe 66 and an discharge pipe 67 connected thereto. The suction pipe 66 has a suction valve 68, and the discharge pipe 67 has an discharge valve 69. Additionally, the piston 61 is elastically supported by a resonance spring 70.
When power is continuously supplied via a motor driver (not shown) to a linear motor 71 comprising the outer yoke 63, the stator coils 64, and the magnets 62, the piston 61 reciprocates in its axial direction to suck and compress a refrigerant in the compression-chamber 65.
For efficient driving, the linear compressor must be driven with a resonance frequency. The resonance frequency of the linear compressor is determined by (1) the elasticity of a mechanically installed elastic member and a compressed gas if the compressor includes this elastic member or by (2) only the elasticity of the compressed gas if the compressor uses only this elasticity of the compressed gas.
In either case, however, the elasticity of the compressed gas varies significantly with variations in loads, so that the resonance frequency of the linear compressor cannot be uniquely determined. A method has thus been used which attempts to calculate the varying resonance frequency using a phenomenon where a resonant state is established when an input current and a piston speed have an equal phase (Japanese Patent Laid-Open No. 10-26083).
Then, an example of such a method will thus be explained in brief with reference to FIG. 8, which is a flow chart useful in explaining a resonance following operation of a conventional linear compressor with a position sensor.
When resonance frequency detection control is started, a sine wave current command value Iref input to the linear compressor is created from a driving frequency f in step S20. In step S21, positional information on the piston from the position sensor installed in the linear compressor is used to determine the current velocity Vnow of the piston.
In step S22, a difference in phase between the determined value Iref and the velocity Vnow is determined. If the phase of the value Iref is faster than that of the velocity Vnow, the process proceeds to step S23. If the phases are equal, the process proceeds to step S24. If the phase of the value Iref is slower, the process proceeds to step S25.
Since in step S22, the current drive frequency is lower than the resonance frequency, the drive frequency f is increased and the process then returns to step S20. Since in step S23, the current drive frequency and the resonance frequency are equal, the process returns to step S20 without changing any drive frequency f. Since in step S24, the current drive frequency is higher than the resonance frequency, the drive frequency f is reduced and the process then returns to step S20.
In this manner, the positional information on the piston obtained from the position sensor has been used to control the drive frequency so as to equal the resonance frequency.
Using this method, however, requires the displacement of the piston in the cylinder to be measured as described above, thereby requiring a displacement measuring device to be integrated into the linear compressor. Consequently, only the volume of the linear compressor not only increases by an amount corresponding to the volume of the displacement measuring device, but also the displacement measuring device itself must be enclosed in a shell of the linear compressor, and there is a problem that an operating reliability of the displacement measuring device must be ensured under hard operational conditions for temperature, pressure or the like.
In view of the above conventional problems, it is an object of the present invention to provide a linear compressor driving device that efficiently drives a linear compressor without using the displacement of a piston, medium and information assembly.
One aspect of the present invention is a linear compressor driving device for linear compressor driving a piston in a cylinder by means of a linear motor to generate a compressed gas, comprising:
an inverter for outputting an alternating current to be supplied to said linear motor;
current detecting means for detecting an output current from said inverter;
voltage detecting means for detecting an output voltage from said inverter;
current amplitude value determining means for determining a current amplitude value of said output current;
output power calculating means for calculating an output power from said inverter based on said detected output current and said detected output voltage;
frequency determining means for determining a frequency of said output current such that said output power is maximum; and
inverter controller for controlling said inverter based on said determined current amplitude value and said determined frequency.
another aspect invention of the present invention is the linear compressor driving device
wherein said voltage detecting means has:
DC voltage detecting means for detecting a DC voltage input to said inverter; and
output voltage calculating means for calculating the output voltage from said inverter based on a control signal transmitted from said inverter controller to said inverter and on said detected DC voltage.
Still another aspect of the present invention is the linear compressor driving device,
wherein said frequency determining means has two variables including a frequency control period and a frequency variation to compare said output power obtained through an operation with a frequency determined during said frequency control period before last with said output power obtained through an operation with a frequency determined during the last frequency control period, in order to determine a present frequency
(1) by varying said frequency in the same direction as that during said last frequency control period, by an amount corresponding to said frequency variation if said output power has increased, and
(2) by varying said frequency in a direction opposite to that during said last frequency control period, by said amount corresponding to said frequency variation if said output power has decreased.
Yet another aspect of the present invention is the linear compressor driving device, wherein said frequency determining means varies said frequency in said same direction a predetermined number of times or more, and maintains the frequency determined during said last frequency control period if said output power has varied by a predetermined amount or more.
Still yet another aspect of the present invention is the linear compressor driving device, wherein said frequency determining means changes said frequency control period based on a variation in said output power.
A further aspect of the present invention is the linear compressor driving device, wherein said frequency determining means changes said frequency variation based on a variation in said output power.
A still further aspect of the present invention is the linear compressor driving device, wherein said frequency determining means maintains said determined frequency if said determined current amplitude value has varied.
A yet further aspect of the present invention is the linear compressor driving device, wherein said current amplitude value determining means maintains said determined current amplitude value if said output power has varied by a predetermined amount.
A still yet further aspect of the present invention is the linear compressor driving device, wherein said linear compressor is used as part of a refrigerating cycle apparatus, and said current amplitude value determining means determines said current amplitude value based on an ambient temperature of said refrigerating cycle apparatus and a corresponding set temperature.
An additional aspect of the present invention is the linear compressor driving device, wherein said current amplitude value determining means determines said current amplitude value so as to reduce a difference between said ambient temperature and said set temperature.
A still additional aspect of the present invention is the linear compressor driving device, wherein said current amplitude value determining means determines said current amplitude value in a manner such that said calculated output power equals a set power to be input to said linear compressor, the power being set based on said ambient temperature and said set temperature.
A yet additional aspect of the present invention is the linear compressor driving device wherein said current amplitude value determining means gradually increases said current amplitude value when said linear compressor is actuated.
A still yet of the present invention is the linear compressor driving device, wherein said current amplitude value determining means gradually reduces said current amplitude value when said linear compressor is stopped.
A supplementary aspect of the present invention is a linear compressor driving device for linear compressor driving a piston in a cylinder by means of a linear motor to generate a compressed gas, comprising:
an inverter for outputting an alternating current to be supplied to said linear motor;
input current detecting means for detecting an input current to said inverter;
current amplitude value determining means for determining a current amplitude value of an output current of said inverter;
input power calculating means for calculating an input power to said inverter based on (1) said detected input current and (2) a predetermined or detected input voltage to said inverter;
frequency determining means for determining a frequency of the output current of said inverter such that said input power is maximum; and
inverter controller for controlling said inverter based on said determined current amplitude value and said determined frequency.
A still supplementary aspect of the present invention is a medium which can be processed by a computer to carry programs and/or data for causing the computer to execute all or some of functions of all or some of the means of the present invention.
A yet supplementary aspect of the present invention is an information assembly comprising programs and/or data for causing a computer to execute all or some of functions of all or some of the means of the present invention.